The expression of a minority of genes involves a substantial proportion of ribosomes shifting reading frame at specific site(s). This frameshifting occurs at shift-prone sites and is commonly greatly stimulated by signals embedded elsewhere in the mRNA, often nearby; i.e. it is programmed. It is proposed to computationally identify candidates for utilized frameshifting in vertebrates especially mammals, and experimentally test them. The goal is to determine the roles of this type of recoding in mammals. Another type of recoding is the dynamic programming of stop codons. Cases where the redefinition involves insertion of a standard amino acid, rather than selenocysteine, will also be similarly investigated. Finally, the extent and function of slippage of RNA polymerase slippage at runs of repeat bases will be assessed. Some occurrences of translational and transcriptional slippage-prone sequences will not be utilized for gene expression and their consequences will be solely errors. The extent of these errors will be investigated. [unreadable] [unreadable]